Tips to show similarities in files

Question

In a project, I found some css files that \"smell\" like there are copy-pasted rules in them.

I wonder what are your strategies for detecting copy-paste stuff in files.

Answer 1

Try Simian.

It is used for copy-paste-detection in source code (Java, C#, C, C++, COBOL, Ruby, JSP, ASP, HTML, XML, Visual Basic, Groovy), but you can run this on plain text files too.

Answer 2

There is a Copy-Paste Detection (CPD) project on sourceforge; http://pmd.sourceforge.net/cpd.html

But even in large projects I find my own knowledge of the code to be a reliable (although not foolproof) detection mechanism.

Also see this question for other suggestions.

Answer 3

Our Semantic Designs CloneDR is a tool that detects copy-paste-edit blocks of code, for many languages: C, C++, Java, C++, COBOL, ECMAScript, PHP, VB6, VB.net, ...

It does using language-accurate parsers to build abstract syntax trees, corresponding to exact program structures, which are then compared for similarity. This means it is not confused in any way by whitespace, formmatting, comments, or even different "spelling" of literals (e.g., 3.14159 is the same as .00314150E3).

It generates a report that shows exactly how the blocks of code are similar, and precisely how they vary. You can see sample reports at the link.